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Sprint projectOct 25, 2026Hong Kong

Same Game, Different Players: A Human-Calibrated Testbed for Cartel Enforcement on LLM Pricing Agents

Julian Mündelein · Team CartelBench

Submitted to AI Collusion Research Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.

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Report: Same Game, Different Players: A Human-Calibrated Testbed for Cartel Enforcement on LLM Pricing Agents

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I replay a published cartel laboratory experiment (Bigoni et al., 2012) with LLM pricing agents under the same payoffs, rules and matching, so every result sits next to the human one, across four models from three families, with every round pre-registered. Told fines, leniency and rewards remove explicit cartels from the agents more than they did from students, yet three of four models keep prices well above the competitive level almost without a word. A price screen lowers these silent prices, but its published threshold becomes the market price: Claude Sonnet 5.5 prices exactly on the threshold at every level from 3 to 6. A secret random threshold removes the bunching but not the high prices. Code, run records and a hashed run ledger are public.

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Cite this project

@misc{mundelein2026same,
  title = {{Same Game, Different Players: A Human-Calibrated Testbed for Cartel Enforcement on LLM Pricing Agents}},
  author = {Julian Mündelein},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/same-game-different-players-a-humancalibrated-testbed-for-cartel-enforcement-on-llm-pricing-agents-uv2e}},
  url = {https://apartresearch.com/sprints/projects/same-game-different-players-a-humancalibrated-testbed-for-cartel-enforcement-on-llm-pricing-agents-uv2e}
}

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